In some video surveillance applications, there exists a need to “blank out” areas of a scene to prevent viewing of objects within these areas. The most basic version of this masking function is known as “window blanking.” The purpose of window blanking is to allow a surveillance system administrator to mask out specific objects within camera viewing areas. That is, objects within these areas cannot be seen on system monitors by surveillance system operators. This feature is desired in applications where privacy is necessary in the scene (e.g. masking of apartment and hotel windows). The number, shape and size of blanking areas that can be set up are dependent upon the specific system.
In window blanking, a rectangular area of a field of view on a monitor or display, commonly referred to as a “window”, is specified by the system. The video signal routed to the monitor or display is then blocked or shielded from view on a portion of the display monitor corresponding to such window. Thus, a window in a particular field of view may be masked or “blanked.” In known surveillance camera systems that provide a basic window blanking function, masked areas remain fixed relative to the scene. If a controllable camera is moved (panned and/or tilted), the masked areas will also move when viewed on a monitor. Likewise, if there is a masked area in the camera view and the camera lens is controlled to zoom in telephoto, the blanked areas will become larger (or smaller when zooming out wide). In all the above scenarios, all objects within the masked areas can never be seen by surveillance system operators, regardless of pan, tilt and zoom position.
However, one drawback of known window blanking systems is that the blanking window must be specified for a particular scene or view, taken or viewed at a particular zoom setting or magnification. This requires a user to first navigate the camera settings to adjust the view to exactly the point where blanking is to occur, and then set and activate the blanking feature. It is desirable to instead allow the general surveillance landscape to be viewed at any camera setting, and at any zoom setting, when deciding and indicating an object in view to be blanked. It is further desirable to specify the blanking window relative to such object, including a specific zoom setting range wherein blanking would be active. As such, it is desirable to provide a system and method of video surveillance which incorporates all of the foregoing features.
Another problem with window blanking occurs when the motion of a typical pan and tilt camera is added to the functionality of the surveillance system. The basic window blanking feature is practical when no rotation of the viewing apparatus is possible. The specified window simply changes overall size given the particular zoom magnification entered into the system. Very little distortion occurs to the objects tracked by the blanking window. However, once rotation is added, and especially if a two degree of freedom pan and tilt camera is used, the objects cannot be easily tracked for blanking due to spherical distortion. To correct for such spherical distortion, it is desirable to provide a system and method of video surveillance which allows for the effective tracking and blanking of objects in a field of view for a pan and tilt camera system.
Finally, another problem with known window blanking systems is that the particular masking object used are either solid, completely masked, or consist of white, black or grayscale blocks. The masking object does not allow a viewer to discern any information about the window blanked by such masking object. Oftentimes however, although privacy is still required for a particular viewing area, some basic information is still desirable, for example, a system which allows detection of movement within a blanked area without revealing details within a scene. As a specific example, in a retail store, it may be desirable to monitor individuals entering and/or leaving a fitting room or restroom. It is desirable therefore, to provide a method and system for video surveillance wherein movement is detectable within a particular blanking area of a field of view, without revealing a threshold level of detail in such area.